Low poly head

I did a test import into Sculptris and did one level of subdivide.
Sculpted on it about ten minutes or so.
I will work on the original mesh and then export again, then back into Nvil to see how it goes.

Nice to see, that you're learning your way through Nvil. When you going to redo the topoly for this guy, you could take a look at some references for edge loops. There's quite a lot, some topologies are called XT, others CT and so on. I am telling you this, because you have poles in areas that may lead to ugly deformations when animated or subdivided. Most of the topologies have in common, that a loop goes from forehead around the eyes and above the nose, and another loop circles around the mouth also going over the nose bone. You'll see it if you look at the references.
I am no expert on characters, because my work mainly concerned environment art. That's why I also searched for references when trying out the retopo tool in NVil. If you search the web for edge loops, you'll easily see what reference I was using.

I am not quite happy with some poles in the mouth area. The sculpting was done in sculptris.

Nice to see, that you're learning your way through Nvil. When you going to redo the topoly for this guy, you could take a look at some references for edge loops. There's quite a lot, some topologies are called XT, others CT and so on. I am telling you this, because you have poles in areas that may lead to ugly deformations when animated or subdivided. Most of the topologies have in common, that a loop goes from forehead around the eyes and above the nose, and another loop circles around the mouth also going over the nose bone. You'll see it if you look at the references.
I am no expert on characters, because my work mainly concerned environment art. That's why I also searched for references when trying out the retopo tool in NVil. If you search the web for edge loops, you'll easily see what reference I was using.

I am not quite happy with some poles in the mouth area. The sculpting was done in sculptris.

thanks for the reference and information.
This head model was for testing and learning NVIL.
Also I thought I would try to see if I could model a head from a sphere and then change the edge flow as I went along. I usually model all the loops and then fill in the rest. From time to time I plan to experiment with the sphere method, because it was very quick for creating a base mesh head and good practice for redirecting edge flow. I think after I refine the sphere method it will be a very fast way to model a character.  I still need to simplify the work flow and use correct topology.

Here are a couple of good links for topology.
http://lightwiki.com/forum/modeler/39-subdivisionmodeling-com-the-pole?limit=10&start=30

http://gregory.kramida.home.comcast.net/~gregory.kramida/AlgoTutorials/TopologyGuide/AnimationTopology.html